Runner's High - Not what you think it is

Runner’s high. That sense of euphoria or “peace with the world” feeling that one gets from a good long run. It has long been attributed the production of endorphins (endogenous morphines) that we produce in response to exercise. Indeed, repeated studies have shown that blood levels of endorphins go up with exercise, particularly endurance exercises like running.

However, there is a problem with this theory. Endorphins cannot cross the blood-brain barrier (BBB) therefore would have no effect on “getting high”. Opioid drugs on the other hand do cross the BBB and induce a feeling of euphoria.

Of course, it is possible that brain levels of endorphins also go up with exercise, but this is very difficult to measure. In a new study, researchers used drugs that block the endorphin/opioid receptor in the brain and showed that they had no effect on the feeling of “runner’s high”.

What then causes runner’s high? Well, the researchers didn’t have look much further than good old marijuana. It turns out that our bodies also produce endocannabinoids (think endogenous THC). It turns out that blood levels of endocannabinoids also go up with exercise AND they can cross the BBB. A direct test of this hypothesis in humans is not possible because drugs that block the brain’s endocannabinoid receptors are not safe in humans. However, they can be used in mice. Blockage of the endocannabinoid pathway in mice also blocks the mouse equivalent of runner’s high (the mice are just as anxious and “twitchy” after exercise as they were before). On the other hand, blockage of the endorphin pathway has no effect on murine runner’s high.

So there you go. Runner’s high exists, but not due to the so-called endorphin rush. More like eating an edible.

This post relied heavily on this New York Times article.

Best, Dr Jeff